On Tue, 2009-09-01 at 16:27 -0400, Theodore Tso wrote: > On Tue, Sep 01, 2009 at 02:44:55PM -0400, Christoph Hellwig wrote: > > On Tue, Sep 01, 2009 at 08:38:55PM +0200, Peter Zijlstra wrote: > > > Do we really need a tunable for this? > > > > It will make increasing it in the field a lot easier. And having deal > > with really large systems I have the fear that there are I/O topologies > > outhere for which every "reasonable" value is too low. > > > > > I guess we need a limit to avoid it writing out everything, but can't we > > > have something automagic? > > > > Some automatic adjustment would be nice. But finding the right auto > > tuning will be an interesting exercise. > > The fact that limit is on a per-inode basis is part of the problem. I would think that it would be a BDI based property, since it basically depends on the speed of the backing dev you're writing to. > Right now, we are only writing out X pages per inode, so depending on > whether we have one really gargantuan inode that needs writout, or ten > big inodes which are dirty, or million small inodes, the fact that we > are imposing a limit based the number of pages in a single inode that > we will write out seems like the wrong design choice. Agreed, number of chunks, where a chunk is some optimum write size for the device in question, and number of seeks, seem a more suitable criteria. Basically limiting the time spend on writeout and not much else. > So perhaps the best argument for not making this be a tunable is that > in the long run, we will need to put in a better algorithm for > controlling how much writeback we want to do before we start > saturating RAID arrays, and in that new algorithm this tunable may no > longer make sense. Fine; at that point, we can make it go away. For > now, though, it seems to be the best way to tweak what is going on, > since I doubt we'll be able to come up with one magic number that will > satisfy everyone. Thing is, will this single tunable be sufficient for people who have both a RAID array and an USB stick on the same machine? -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
